1. Field of the Invention
The present invention relates to a flanged metal pipe (a metal pipe with a flange at an end thereof) and a manufacturing method thereof. In particular, the present invention relates to a flanged metal pipe that is excellent in rigidity, strength and durability, and a manufacturing method thereof.
2. Description of Background Art
It is rather unusual to use a simple tubular metal pipe structure for building materials such as metal pipe poles, for construction materials such as rotary press-in metal pipe piles and for industrial materials such as liquid transporting pipes. Typically, for one of the purposes mentioned above, a separately made flange portion is welded to an open end of the tubular metal pipe to form a flanged metal pipe.
For example, in the case of using a flanged pipe for industrial materials such as liquid transporting pipes, the flange portion is welded to an open end of the metal pipe body and projects outwards. The flange portion is then butt-jointed to a same-shaped flange portion of another flanged metal pipe by a fastener.
In the case of using a flanged metal pipe as a metal pipe pole, the flange portion is also welded to an open end of the metal pipe body and projects outward. The flanged metal pipe can function as a metal pipe pole by fixing the flange portion to a base plate using a bolt.
In the case of using a metal pipe as a rotary press-in metal pipe pile, a disk-shaped member is welded to an open end of the metal pipe body to form a rotary excavating blade.
In addition, a method of continuously forming a flange portion at an end of a metal pipe as an extended portion of the pipe by rolling an open end portion of the metal pipe using a cone-shaped roll is known. In such a flanged metal pipe, the flange portion is a plastically deformed disk-shaped or truncated-cone-shaped portion at the end of the metal pipe, which is continuously formed by cold working (rolling) to an open end portion of the metal pipe.
However, the metal pipe according to the background art has been previously subjected to a special pre-processing to increase a thickness of an open end portion by hot working (rolling). In addition, in the background art, a metal pipe having a continuously formed flange portion has not been used without using a separate fastening device. Furthermore, a metal pipe having a continuously formed flange portion has not been used as a metal pipe pole by fixing the flange portion to a base plate using a bolt. In other words, in the background art, it is not known to use a metal pipe having a continuously formed flange portion by a cold rolling process as a conventional flange that has a bolt hole to allow a bolt to fix the flanged pipe to other members.
A flanged metal pipe obtained by forming an open end portion of the metal pipe into a disk-shaped flange or a truncated-cone-shaped flange in a cold rolling process are not known to be used as a flange portion to be fixed to other members or structures using a bolt through the hole formed in the flange. The reason why such a metal pipe is not used in the above manner is that a flange portion of the flanged metal pipe is insufficient in rigidity, strength and durability to be fixed to other members or structures by a bolt through the hole formed in the flange portion.